1. Field of the Invention
This invention relates to an apparatus of improved operability for controlling an engine in a hydraulically driven vehicle.
2. Description of the Prior Art
It has been a drawback of a conventional hydraulically driven vehicle, such as a power shovel, that the rotating speed of an engine set by a fuel control lever is maintained even when the vehicle is not working, resulting in a waste of fuel.
In order to improve this drawback, the applicant has proposed in Japanese Utility Model Application Provisional Publication No. 58-156138 an apparatus for controlling the engine of a hydraulically driven vehicle, including a pair of hydraulic pumps b and d driven by the engine a for supplying a hydraulic pressure to a travel circuit and a work circuit, respectively and a fuel control lever e which actuates a control lever f for a governor c to thereby set the rotating speed of the engine a, and characterized in that the governor control lever f is provided with a drive cylinder g which holds the governor control lever f in an engine idling (or low speed) position when the hydraulic pumps b and d are not under load, and drives it into a full engine speed position when those pumps are loaded. This apparatus is shown in FIG. 1.
As this apparatus relies upon the output pressure of the hydraulic pumps b and d for urging the governor control lever f toward its full engine speed position, however, an undesirable low speed rotation (or idling) of the engine is likely to result from a variation in the hydraulic pressure available. When a work machine is lowered, for example, it is impossible to obtain a sufficiently high hydraulic pressure, as the machine tends to come down by its own weight. The same problem occurs when a swing structure rotates by inertia. Thus, a reduction in the pressure rotating the governor control lever f toward its full engine speed position allows a spring force to urge the lever f toward its idling position and thereby lower the rotating speed of the engine.
Moreover, if all of the control levers are brought to their neutral positions, the resulting absence of the pressure urging the governor control lever f toward its full engine speed position brings about an immediate reduction in the rotating speed of the engine. This gives rise to a time lag in operation for any subsequent work and a lowering in control performance. It is necessary but undesirable from the standpoint of a noise to raise the engine speed repeatedly.